Because the sentencing is after the House rises, but before it is officially dissolved, if Banks is convicted MPs face the prospect of being recalled to the capital from the general election campaign trail to vote on whether to hold a by-election in his Epsom seat.

A legal expert said today that could be averted if Banks resigned before the House rose.

Key said he was not in a position to offer the former Auckland mayor advice.

"It's not for me to offer a view on that," Key said in Nelson this morning.

"In the end he is the leader of another political party.

"I can't offer him advice any more than I could offer David Cunliffe advice on whether he should resign."

Asked about Cunliffe's claims that the Government was being propped up by a "corrupt" politician, Key said Cunliffe should rule out working with the Internet Party.

"I'm not going to be lectured by David Cunliffe," he said.

"If he was the man of principle he says he is, he'd be ruling out the Internet Party and Kim Dotcom who's before the court and is a convicted fraudster, but he's not going to do that. Most people will see it for what it is, which is politics."

Key said the Banks matter was before the courts so he could not comment, but he maintained that in his dealings with ACT's sole MP, he had always found Banks to be "honest".

Asked whether it was possible that MPs would be recalled after the House rose, Key described the question as "technical" and said it was a moot point because he did not believe any MPs would want a by-election so close to the general election.

Asked if he would declare that National would consider ruling out using Banks' vote for the remainder of the term, Key appeared to suggest it would be considered.

"We have confidence and supply from a bigger group of parties than just the ACT Party, so we'll give some consideration to that matter, but I've just got back from overseas and haven't really had a chance to consider that."